There has been recent interest in improving performance characteristics of athletic and walking shoes. Initially these efforts were primarily directed to improving cushioning and shock absorption. Improvement of these characteristics was materially assisted with the development of a range of synthetic materials particularly useful in footwear manufacture. Most recently, microcellular closed cell material of selected compressibilities such as ethylene vinyl acetate (EVA) and improved polyurethane systems has been used in the commercial manufacture of a variety of midsole and wedge components intended to improve the comfort, cushioning and shock absorption of footwear. Commercially available footwear using such material now include components to improve the stability and bio-mechanics of the footwear. Such components as motion control devices and torsional rigidity bars are also now common components in such commercial products.
The most recent industry interest relates to the manufacture of footwear having energy return characteristics. This interest has also been enhanced by the common availability of EVA and other microcellular foam materials for use as resilient cushioning material. Such material has the characteristic of absorbing energy in the compression phase of a gait cycle and releasing the energy as the compression is released. The absorbed energy is released in the push-off phase of the gait cycle in running or walking.
Other energy return systems have contemplated the use of thermoplastic hollow tubes or shapes encapsulating a fluid or gas such as a Freon. These encapsulations are strategically located in the midsole or elsewhere to provide an energy return mechanism to the shoe.
Still other systems contemplate the use of such commercially available materials as Hytrel and Kevlar in various blends, compositions and molded arrangements positioned in the arch and/or medial portion of the shoe providing mechanical cushioning and energy storage.
There has been some use of netting or mesh arrangements in selected portions of a sole construction for various purposes. Insofar as the applicant is aware, the earliest of such efforts was in the form of a fine woven wire fabric described in U.S. Pat. No. 812,496 issued Feb. 13, 1906. Mesh used in that construction, however, provided only stiffness and wearing qualities at the bottom of the heel. That patent failed to suggest arranging the mesh under appropriate tension and thus fails to teach or suggest the use of such mesh in an energy return system.
A second disclosure of a mesh construction is contained in U.S. Pat. No. 1,650,466 issued Nov. 22, 1927. In that construction, a fabric of mesh is used to retain the shape of a component and does to act as an energy return system such as a spring or the like.
Most recently, U.S. Pat. No. 4,297,796 issued Nov. 3, 1981, discloses the use of an open work support or netting of stretch resistant threads secured to the top side of a flexibly deformable sole layer. This netting structure is intended to distribute shock stresses in the heel or ball of the foot. Since that open mesh is three-dimensional, it redistributes deformation of the sole structure under compression and does not function as a spring-like energy return system.
Similarly, a more recent disclosure in U.S. Pat. No. 4,608,768 issued Sep. 2, 1986 discloses the use of an open work structure embedded in a resilient member with plugs arranged within the openings of the open work structure. In such an arrangement, different shock absorbing characteristics may be imparted to selected portions of the sole structure. The mesh arrangement, itself, however does not appear to be used as a spring-like energy return system.
Other references in which various midsole structures having related arrangements include, U.S. Pat. Nos. 3,808,713, 4,179,826, 4,263,728, 4,451,994, 4,507,879, 4,566,206, 4,753,021, and 4,774,774.
Insofar as the applicant is aware, no efforts have been made to use a mesh or net-like structure as a means for imparting energy return characteristics in footwear. Prior efforts directed toward energy return systems have, insofar as the applicant is aware, centered upon the use of macro and microcellular structures in which energy is stored in a fluid system under compression and thereafter released during expansion of the fluid component. Such arrangements have a variety of limitations. Nor is applicant aware of using a mesh-like arrangement in combination with a frame shaped to provide added functions and features including cushioning and stability.